Meteorological Phenomena: Polar Aurora

Polar aurora is one of the most beautiful phenomena a person can imagine and whitness (if lucky). I find that its appearance is a complete opposite from the places it can be seen. Such a vibrant, floating and heavenly sight is only possible to catch glimpse of in the most weather tormented areas of our planet, whipped by the cold and severe winds. But first of all, let’s categorize this appearance in the meteorological terms. Polar aurora fals in the category of electrometeors. Electrometeor is a visible or audible manifestation of the atmospheric electricity. As for our most beautiful electrometeor, polar aurora is a luminous phenomenon which appears in the high atmosphere in the form of arcs, bands, draperies or curtains. The general name aurora comes from the Latin word aurora, which means sunrise and the second part of the two specific types of aurora I will mention later on. Polar aurorae are formed as a result of following actions. When fast electrically charged particles (electrons) are shot out from the sun during solar eruptions, they slam into atoms and molecules of the higher atmosphere (thermosphere). Those particles from space are channeled by the earth‘s magnetic field which means that polar aurorae are most frequently observed in the vicinity of the magnetic poles. The auroral zone is typically 10° to 20° from the magnetic pole. As I have mentioned, there are two types of aurorae. In the northern latitudes we have aurora borealis (northern lights) which most of this text refers to. It is named after the Roman goddess of dawn (Aurora, hence the sunrise mentioned at the beginning of the post) and after the Greek name for the north wind (Borealis). Besides this most mentioned type of aurora, we have its southern counterpart in the southern latitudes called the aurora australis (southern lights) with almost identical features of the northern lights. These are visible from high southern latitudes in Antarctica, South America, New Zealand and Australia (including Tasmania). The luminance of polar aurorae is very variable. It is often comparable with that of clouds illuminated by the full moon but may occasionally be much greater. The color of polar aurora is in the most cases white with greenish or greenish-yellow tinge. Tinges do vary. The green light of aurora has a precisely defined color in the spectrum (“narrow spectral line”). Such precise colors are usually the signatures of the atoms which emit them. The green light of the aurora was a mystery to scientists for years because it did not fit any known element. It turned out to be produced by oxygen atoms, but under conditions that in our atmosphere only exist in the very rarefield upper levels. A red aurora, which is quite rare, arises at even greater heights and is also produced by electrons hitting oxygen.